Long-Term Changes of Polar Activity of the Sun

We discuss long-time changes of polar activity of the Sun using the new observational data sets in the optical range during 1872–2001. A study of the secular and cycle variations of the magnetic activity at the high-latitude regions is the main goal that includes polar magnetic field reversals during 1872–2001 and secular changes of the duration of polar activity cycles. The secular increase of the area of polar zones during the minimum activity in the last 120 years and as consequence a decrease of coronal temperature of the Sun in the high-latitude zones during the last 50 years. Correlation between the polar cycles of Caii-K bright points with the Wolf sunspot numbers cycles, W(t), and the 22-year polar magnetic cycles of Caii-K bright points at the high latitudes during 1905–1995 is discussed.     

Self-similar solutions for the blast wave problem in radiative gasdynamics,I

Similarity solutions, describing the flow of a perfect gas behind spherical shock waves, are investigated including the radiation heat flux. The shock is assumed to be propagating in a medium at rest. Shock radius varies exponentially with time and density is inversely proportional to fifth power of the shock radius immediately ahead of the shock front.     

Thermal stability of a layer with permeable boundaries and variable gravitational field

The aim of this paper is to investigate the thermal stability of a fluid layer with permeable boundaries and a variable gravitational field. It is observed that the principle of exchange of stabilities is valid when the layer is heated form below and the complex growth rate of an arbitrary oscillatory mode exists outside of a circle whose radius depends upon the permeability parameter, Prandtl number and wavelength of the mode. In the case of a layer heated from below, gravity increasing upward has a destabilizing effect whereas the permeability parameter has a stabilizing effect.     

The exact theory of inductive conductivity sensors for oceanographic application

The results of a general theoretical investigation of three commonly used types of inductive conductivity sensors, i.e., the single transformer, the double transformer, and the double transformer with an additional loop, are presented. The resulting formulas describe the dependence of the sensor output signal not only on the conductivity of the seawater but also on the parameters of the electrical circuit, among them the permeability of the transformer core(s), which-unlike the other parameters-shifts considerably during oceanographic in situ measurements. A mathematical discussion of these formulas shows that for certain circuit configurations, the sensor output is independent of changes in permeability. Most of these configurations form the basis of existing oceanographical conductivity sensors, among them the "classical" sensors developed by H. Hinkelmann [3], [4], and by N. L. Brown [14], while some others make evident further possibilities for eliminating the unwanted effects of shifting permeability. In the era of microelectronics, the latter might lead to a reassessment, especially of the single transformer-type sensor.     

Nature of the Martian uplands: Effect on Martian meteorite age distribution and secondary cratering

Abstract— Martian meteorites (MMs) have been launched from an estimated 5–9 sites on Mars within the last 20 Myr. Some 80–89% of these launch sites sampled igneous rock formations from only the last 29% of Martian time. We hypothesize that this imbalance arises not merely from poor statistics, but because the launch processes are dominated by two main phenomena: first, much of the older Martian surface is inefficient in launching rocks during impacts, and second, the volumetrically enormous reservoir of original cumulate crust enhances launch probability for 4.5 Gyr old rocks. There are four lines of evidence for the first point, not all of equal strength. First, impact theory implies that MM launch is favored by surface exposures of near‐surface coherent rock (≤10² m deep), whereas Noachian surfaces generally should have ≥10² m of loose or weakly cemented regolith with high ice content, reducing efficiency of rock launch. Second, similarly, both Mars Exploration Rovers found sedimentary strata, 1–2 orders of magnitude weaker than Martian igneous rocks, favoring low launch efficiency among some fluvial‐derived Hesperian and Noachian rocks. Even if launched, such rocks may be unrecognized as meteorites on Earth. Third, statistics of MM formation age versus cosmic‐ray exposure (CRE) age weakly suggest that older surfaces may need larger, deeper craters to launch rocks. Fourth, in direct confirmation, one of us (N. G. B.) has found that older surfaces need larger craters to produce secondary impact crater fields (cf. Barlow and Block 2004). In a survey of 200 craters, the smallest Noachian, Hesperian, and Amazonian craters with prominent fields of secondaries have diameters of ?45 km, ?19 km, and ?10 km, respectively. Because 40% of Mars is Noachian, and 74% is either Noachian or Hesperian, the subsurface geologic characteristics of the older areas probably affect statistics of recognized MMs and production rates of secondary crater populations, and the MM and secondary crater statistics may give us clues to those properties.     

Old Pulsators: White Dwarfs and Their Immediate Precursors

There are now fully six classes of pulsators among white dwarfsand their immediate precursors among central stars of planetarynebulae and on the extended horizontal branch.In this review, we outline those observational and theoreticalconsiderations that link them together and set them apart fromother kinds of pulsating stars.We summarize some select astrophysical puzzles to which studiesof such pulsators might speak, and we discuss current applicationsin the fields of atomic, nuclear, and neutrino physics.Finally, we suggest how future observing programs might solve somegeneral problems common not only to the white dwarf and pre-whitedwarf pulsators but to many types of variable stars.